The present invention relates to an angular type ball bearing which is used in a rotation support portion included in various machines and apparatus, especially in the spindle main shaft portion of a machine tool to support loads in radial and thrust directions and, in particular, to a structure for improving the lubricating performance of the spindle main shaft portion of the machine tool.
Further, the present invention also relates to a shaft support structure with the above-mentioned angular type ball bearing.
Referring here to FIG. 11, recently, as a shaft support structure 80 which is applied to the spindle main shaft portion of a machine tool, there is known a structure in which, between the outer peripheral surface of a main shaft 81 and the inner peripheral surface of a housing 82, there are arranged a plurality of angular type ball bearings 90 (which is hereinafter referred to as a bearing 90 simply) side by side along the axial direction of the main shaft 81.
Between the inner rings 91 of the respective bearings 90, there are interposed inner-ring-spacers 83 respectively. Also, between the outer rings 92 of the respective bearings 90 as well as between the outer ring 92 of the bearing 90 that is located in the end of the bearings 90 and a cover body fixed to the left end portion (in FIG. 11) of the housing 82, there are interposed outer-ring-spacers 85 respectively.
Each bearing 90 is structured such that a ball row 93 is rollably inserted together with a retainer 94 into a raceway formed between the inner ring 91 and outer ring 92 and, in the anti-load-side portion of the outer ring 92, there is formed a counter bore 96 for enhancing the oil discharge performance of the bearing 90 (more specifically, in the case of the two bearings 90 that are arranged on the left side in FIG. 11, in the portions thereof that are situated on the left-hand side of balls 95 in the ball rows 93, there are respectively formed counter bores 96; and, in the case of the two bearings 90 that are arranged on the right side in FIG. 11, in the portions thereof that are situated on the right-hand side of the balls 95, there are respectively formed counter bores 96). That is, due to provision of the counter bores 96, the oil discharge performance of the respective bearings 90 in discharging lubricating oil is enhanced to thereby be able to reduce the required rotation torque of the main shaft 81.
In the above-mentioned conventional shaft support structure 80, in order to improve the oil discharge performance of the respective bearings 90 as well as reduce the required rotation torque of the main shaft 81, there are formed the counter bores 96 in the anti-load side portions of the outer rings 92 of the respective bearings 90.
However, the counter bores 96 of the bearings 90 are respectively very small as the lubricating oil discharge spaces. For this reason, especially, to support the main shaft 81 of a machine tool, the oil discharge performance of the bearings 90 is insufficient, which makes it impossible to secure the proper lubricating performance of the bearings 90.
This raises a problem that a rise in the temperatures of the bearings and the required rotation torque of the shaft to be supported cannot be reduced. That is, failure to reduce a rise in the bearing temperature and the shaft required rotation torque makes it impossible to secure the high working precision of the machine tool.
Also, the cover body 84 is fixed to the left end portion (in FIG. 11) of the housing 82 through a bolt, and the outer rings 92 of the bearings 90 are respectively fixed in the thrust direction by the cover body 84 through their associated outer-ring-spacers 85.
However, when the tightening amount of the cover 84 to the housing 82 becomes excessively large, there is a fear that the outer rings 92 of the bearings 90 can be deformed. In case where the outer rings 92 of the bearings 90 are deformed, there arises a problem that the raceway surfaces of the outer rings 92 forming the raceways for the balls 95 can be deformed, thereby lowering the running accuracy of the main shaft 81.
On the other hand, when the tightening amount of the cover 84 to the housing 82 becomes excessively small, although there is reduced the fear that the outer rings 92 of the bearings 90 can be deformed, the creep and contact rigidity of the outer rings 92 are affected.
In view of the above, the tightening amount of the cover body 84 to the housing 82 is set in the range of 10-30 xcexcm based on previous results. However, in fact, there cannot be avoided the deformation of the outer rings 92 of the bearings 90. Therefore, there is still left the problem that, due to the deformation of the raceway surfaces of the outer rings 92, the running accuracy of the main shaft 81 is degraded.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional angular type ball bearing.
Accordingly, it is an object of the invention to provide an angular type ball bearing which is simple in structure, can reduce the manufacturing cost thereof, and can secure the proper lubricating performance of a shaft to be supported thereby, whereby the bearing temperature rise reduction and the shaft required rotation torque reduction can be achieved as well as the running accuracy of the shaft to be supported thereby can be improved.
According to the invention, the above object can be attained by the following structures that are respectively set forth in the following first to fifth aspects of the invention.
In the first aspect of the invention, an angular type ball bearing structured such that a ball row is rollably inserted together with a retainer in a raceway formed between an inner ring and an outer ring, wherein the anti-load-side end portion of the outer ring is situated nearer to rolling bodies (balls) existing along the axial direction of a shaft to be supported by the bearing than the load-side end portion of the inner ring.
In a second aspect of the present invention, an angular type ball bearing structured such that a ball row is rollably inserted together with a retainer in a raceway formed between an inner ring and an outer ring, wherein the anti-load-side end portion of the outer ring is situated nearer to rolling bodies (balls) existing along the axial direction of a shaft to be supported by the bearing than the load-side end portion of the inner ring, and the anti-load-side end portion of the inner ring is situated nearer to the rolling bodies existing along the axial direction of the shaft to be supported by the bearing than the load-side end portion of the outer ring.
In a third aspect of the invention, a shaft support structure in which the angular type ball bearings set forth in the above first or second aspect are disposed in two or more rows side by side along the axial direction of a shaft to be supported by the ball bearings between the outer peripheral surface of the shaft to be supported and the inner peripheral surface of a housing, inner-ring-spacers are respectively interposed between the inner rings of the bearings in the respective rows, and outer-ring-spacers are respectively interposed between the outer rings of the bearings in the respective rows as well as between the outer ring of the endmost bearing and a cover body fixed to the end portion of the housing.
By the way, as the material of the inner-ring-spacers and outer-ring-spacers, preferably, material having high thermal conductivity may be used. This can enhance the thermal conductivity of the shaft support structure as a whole as well as can control a rise in the temperature of the angular type ball bearings in the respective rows down to a low level.
In a fourth aspect of the invention, a shaft support structure as set forth in the above third aspect, wherein oil discharge holes for discharging lubricating oil are formed at the given positions of the outer-ring-spacers in the vicinity of the rolling bodies.
In a fifth aspect of the invention, a shaft support structure as set forth in the above third or fourth aspect, wherein oil supply holes for supplying lubricating oil are formed at the given positions of the outer-ring-spacers in the vicinity of the anti-load-side end portions of the outer rings.
The angular type ball bearing as set forth in the first aspect is applied to the support portion of a rotary shaft included in various machines and apparatus and, especially, to the spindle main shaft portion of a machine tool. And, for example, from oil supply nozzles which are disposed in the vicinity of the anti-load-side end portion of the inner ring, there is supplied lubricating oil toward the inner ring and toward between the rolling bodies according to an oil/air lubricating system or an oil/mist lubricating system. The lubricating oil supplied forms films of oil in the contact portions between the inner and outer rings and rolling bodies to thereby lubricate the bearing.
In this lubrication, since the anti-load-side end portion of the outer ring is situated nearer to rolling bodies existing along the axial direction of a shaft to be supported by the bearing than the load-side end portion of the inner ring, there can be provided a large lubricating oil discharge space, so that the excessive lubricating oil in the interior portion of the bearing can be discharged with high efficiency. This makes it possible to reduce-not only a rise in the temperature of the bearing but also the required rotation torque of the shaft to be supported. Also, the outer ring is hard to be deformed and thus the lowered running accuracy of the shaft to be supported, which could be otherwise caused by the deformed outer ring, can be prevented.
According to the angular type ball bearing as set forth in the second aspect, since the anti-load-side end portion of the outer ring is situated nearer to the rolling bodies (balls) existing along the axial direction of a shaft to be supported by the bearing than the load-side end portion of the inner ring, there can be provided a large lubricating oil discharge space, so that the excessive lubricating oil in the interior portion of the bearing can be discharged with high efficiency. Also, because the anti-load-side end portion of the inner ring is situated nearer to the rolling bodies existing along the axial direction of the shaft to be supported by the bearing than the load-side end portion of the outer ring, there can be reduced the influence of an air curtain, so that the lubricating oil can be supplied into the interior portion of the bearing with further higher efficiency. This makes it possible to reduce not only the temperature rise of the bearing but also the required rotation torque of the shaft to be supported. Also, the outer ring is hard to be deformed, which can prevent the lowered running accuracy of the shaft to be supported that could be otherwise caused by the deformed outer ring. In a shaft support structure as set forth in the third aspect, the angular type ball bearings as set forth in the first or second aspect are disposed in two or three rows side by side along the axial direction of a shaft to be supported by the ball bearings between the outer peripheral surface of the shaft to be supported and the inner peripheral surface of a housing. Between the inner rings of the ball bearings in the respective rows, there are interposed inner-ring-spacers respectively. Also, between the outer rings of the ball bearings in the respective rows as well as between the outer ring of the endmost bearing and a cover fixed to the end portion of the housing, there are interposed outer-ring-spacers respectively.
According to the present shaft support structure, for the angular type ball bearings in the respective rows, there is supplied lubricating oil toward the inner rings as well as toward between the rolling bodies from oil supply nozzles disposed between the ball bearings in the respective rows in the vicinity of the anti-load-side end portions of the inner rings according to an oil/air lubricating system or an oil/mist lubricating system. The lubricating oil supplied forms films of oil in the contact portions between the inner and outer rings and rolling bodies to thereby lubricate the ball bearings.
In this lubrication, in case where the anti-load-side end portions of the outer rings of the ball bearings in the respective rows are situated nearer to the rolling bodies existing in the axial direction of the shaft to be supported than the load-side end portions of the inner rings, or in case where the anti-load-side end portions of the inner rings of the ball bearings in the respective rows are situated nearer to the rolling bodies existing in the axial direction of the shaft to be supported than the load-side end portions of the outer rings, the influence of the air curtain can be reduced to thereby be able to supply the lubricating oil into the interior portions of the ball bearings with high efficiency, and also there is provided a large space for discharging the lubricating oil to thereby be able to discharge the excessive lubricating oil in the interior portions of the ball bearings with high efficiency. Therefore, the bearing temperature rise and the shaft required rotation torque can be reduced. Also, the outer rings are hard to-be deformed, which can prevent the lowered running accuracy of the shaft to be supported that could be otherwise caused by the deformed outer rings.
In a shaft support structure as set forth in the fourth aspect, in the respective outer-ring-spacers interposed between the outer rings of the angular type ball bearings in the respective rows as well as between the outer ring of the endmost bearing and a cover body fixed to the end portion of the housing, there are formed oil discharge holes respectively. That is, the oil discharge holes are respectively disposed at the given positions of their associated outer-ring-spacers in the vicinity of the rolling bodies to discharge the excessive lubricating oil in the interior portions of the ball bearings.
Therefore, there can be provided a further larger lubricating oil discharge space, which makes it possible to discharge the excessive lubricating oil in the interior portions of the ball bearings with very high efficiency. Thanks to this, the bearing temperature rise as well as the shaft required rotation torque can be reduced more positively.
In a shaft support structure as set forth in the fifth aspect, in the respective outer-ring-spacers interposed between the outer rings of the angular type ball bearings in the respective rows as well as between the outer ring of the endmost bearing and a cover body fixed to the end portion of the housing, there are formed oil supply holes respectively. That is, the oil supply holes are respectively disposed at the given positions of their associated outer-ring-spacers in the vicinity of the anti-load-side end portions of the outer rings to supply the lubricating oil into the interior portions of the ball bearings.
Therefore, there can be provided a bearing having a pseudo outer ring oil supply system and thus, when compared with a bearing having a conventional outer ring oil supply system in which an oil supply hole is formed directly in the outer ring of the bearing, not only there can be obtained an equivalent effect but also the manufacturing cost of the bearing can be reduced.
Further, the above-mentioned object can also be achieved by a shaft support structure, according to the present invention, comprising:
a plurality of angular type ball bearings which supports a shaft and are aligned in an axial direction of the shaft,
wherein each of the bearings comprising:
an inner ring;
an outer ring;
a ball row defined by a plurality of balls, each of the balls rollably inserted into a raceway formed between the inner and outer rings; and
a retainer disposed between the inner and outer rings and rollably retaining the balls therebetween,
wherein the anti-load-side end portion of the outer ring is situated nearer to the ball row than the load-side end portion of the inner ring in an axial direction of the ball bearing.
In the shaft support structure, it is preferable that a width of the outer ring is larger than a width of the inner ring in the axial direction of the ball bearing.
In addition, in the shaft support structure, it is preferable that the anti-load-side end portion of the inner ring is situated nearer to the ball row than the load-side end portion of the outer ring in the axial direction of the ball bearing.
Further, in the shaft support structure, it is preferable to further comprises:
at least one inner-ring-spacer interposed between the adjacent inner rings; and
at least one outer-ring-spacer interposed between the adjacent outer rings.
Furthermore, in the shaft support structure, it is advantageous to further comprises:
a housing rotatively accommodating the shaft;
a cover fixed to the end portion of the housing in the axial direction of the shaft;
an additional outer-ring-spacer interposed between the endmost outer ring in the axial direction and the cover.
Moreover, in the above-mentioned shaft support structure according to the present invention, it is also advantageous that the inner-ring-spacer and the outer-ring-spacer are made of a material having high thermal conductivity.
Furthermore, in the above-mentioned shaft support structure, it is preferable that atleast one oil discharge hole for discharging lubricating oil is formed at a given position of the outer-ring-spacer in the vicinity of the ball.
In addition, in the above-mentioned shaft support structure, it is preferable that at least one oil supply hole for supplying lubricating oil is formed at given positions of the outer-ring-spacer in the vicinity of the anti-load-side end portion of the outer ring.
Further, in the above-mentioned shaft support structure, it is more preferable that a plurality of oil supply hole are formed at given positions of the outer-ring-spacer in the vicinity of the anti-load-side end portion of the outer ring and are aligned at a predetermined interval in a peripheral direction of the bearing.